‘Nanotechnologies’ cannot be legally reviewed as one single category. In this chapter, the three technologies utilising nanomaterials to be discussed in this book will be introduced in some technical detail: thermobaric weapons, optogenetics and genetic modification. Each use of nanomaterials needs to be considered individually to ensure compliance with existing international laws during war. The three uses of nanomaterials considered in this book have been chosen because they raise different existing international law (illustrating the breadth and depth of existing international law) and finally, because they are each at a different stage of development and use.